There are many devices that are best made of cardboard for their intended purpose, such as a disposable bag-handle grip for plastic grocery bags, a cereal box and a storage case for a tape cassette, such as a Phillips-type audio cassette tape, for example. In such devices there are overlapping panels that are to be locked together conveniently and reliably even after locking and unlocking them repeatedly. When such repetition is expected, the device may be made of heavier weight, solid cardboard, for example, or of more moderate weight, corrugated cardboard consisting of a coarse fluted paper board, i.e., coarse paper board formed to have straight, regular and equally spaced grooves and ridges, with adherent flat paper board on one or both sides to give the fluted paper some rigidity, though still be pliable.
A problem with such devices made of cardboard is providing a way to easily and reliably lock and unlock one panel overlapping another panel and to do so repeatedly without losing the integrity of the locking means, usually provided by a tab extending from the edge of one panel that overlaps the other having a slit into which the tab is inserted, as is commonly done on closing cereal boxes. Thus, once a cereal box has been opened, it may be easily closed with the overlapping panels or flaps locked together by inserting the tab of one flap into the slit of the other. While that provides ease and repeatability with satisfactory reliability for a cereal box, which normally serves out its normal life span on a shelf without any undue stress in relocking the flaps, it might not be satisfactory for boxes destined to serve for more active purposes over an indefinite period, such as a box for a Phillips-type audio cassette, or for more stressful purposes, such as a grip for holding together handles of one or more ubiquitous plastic grocery bags.